786. 第k个数
#include <iostream> using namespace std; const int N = 1e6 + 10; int n, k; int q[N]; int quick_sort(int l, int r, int k) { if (l == r) return q[l]; int i = l - 1, j = r + 1; int x = q[l + r >> 1]; while (i < j) { while (q[++ i] < x); while (q[-- j] > x); if (i < j) swap(q[i], q[j]); } int sl = j - l + 1; if (k <= sl) return quick_sort(l, j, k); return quick_sort(j + 1, r, k - sl); } int main() { cin >> n >> k; for (int i = 0; i < n; ++ i) cin >> q[i]; cout << quick_sort(0, n - 1, k); return 0; }